Typically autonomous systems (e.g. autonomous vehicles) are tasked with achieving goals with reduced (or no) human interaction.
An autonomous system is assessed, or validated, typically by determining whether or not it has the necessary capabilities to support an operator in achieving the task. This validation of an autonomous system is primarily a design-time activity with a focus on ensuring that the system does what a user wants it to do, and that this system is reliable, available, dependable, safe, etc.
However, increasingly autonomous systems are being used in complex and uncertain environments that the system has not been assessed or validated for during the design stage.